Handbook of Solvents - George Wypych - ChemTech - Ventech!

1484 Victor Cherginets
161 E.I. Cooper, E.J.M. O’Sullivan, Proceedings of the 8th international symposium on molten salts; 92,
16, (1992).
162 P.A.Z. Suarez, S. Einloft, J.E.L. Dullius, R.F. de Souza, and J. Dupont, J.Chem.Phys., 95, (1998).
163 M. Ma and K.E. Johnsom, Can. J. Chem., 73, (1995).
164 M.Torres, Unpublished results, Queens University of Belfast, (2000).
21.3 OXIDE SOLUBILITIES IN IONIC MELTS
Victor Cherginets
Institute for Single Crystals, Kharkov, Ukraine
21.3.1 METHODS USED FOR SOLUBILITY ESTIMATIONS IN IONIC MELTS
Processes of the dissolution of metal oxides in ionic melts are accompanied by interactions
between ions of dissolved substance with ions of the melt (solvation). The superimposition
of the mentioned processes results in the formation of metal complexes with the melt anions
and cation complexes with oxide-ions. Therewithal, the definite part of the oxide passes into
the solution without dissociation as uncharged particles. Thus, in saturated solution of oxide
the following equilibria take place:
MeOs = MeOl
[21.3.1]
MeO = Me + O
l
2+ 2−
[21.3.2]
2+ k − 2−ik
Me + iX = MeX
[21.3.3]
i
2− m+
nm−2
O + nKt = Kt O
[21.3.4]
n
where:
s and l subscripts denoting solid and dissolved oxide, respectively,
Me the designation of two-valent metal
Kt m+
the melt cation (such as Cs + ,K + ,Na + ,Ba 2+ ,Ca 2+ , etc.),
X kthe
melt anion (Cl - ,Br - ,I - 2- 3-
,SO4,PO, etc.)
Since at the dissolution of any oxide in melts a degree of interaction “Kt m+ -O 2- ”
should be the same and the complexation with melt anions for cations of oxide may be assumed
as closed, 1 therefore, it can be believed that oxide solubilities depend mainly on the
degree of interactions [21.3.1] and [21.3.2], latter may be considered as an acid-base interactions
as proposed by Lux. 2 The constant of [21.3.2]
K
MeO
a a m m
Me O
= ≈
a m
2+ 2− 2+ 2−
Me O
MeO
MeO
where:
a and m activities and molarities of the particles noted in the subscripts
[21.3.5]
may be considered as a measure of acidic properties of the cation if reaction [21.3.2] is homogeneous.
However, a majority of oxides possess limited solubilities in molten salts and
the excess of the oxide should precipitate. In this case the fixation and removing oxide ions